This application is part of a multicenter clinical trial titled the Prospective Investigation of Pulmonary Embolism Diagnosis-II (PIOPED-II). Pulmonary embolism (PE) is common, yet frequently undiagnosed. Pulmonary angiography is the definite diagnostic test in such patients, but there is hesitancy to use it because of morbidity, discomfort, cost and lack of availability in community hospitals. Serial noninvasive leg doppler examinations reduce the need for pulmonary angiography, and many physicians, incorporate their use in diagnostic algorithms. Irrespective, large numbers of patients would require pulmonary angiography. Contrast enhanced spiral computed tomography (CT) is minimally invasive test that offers the possibility of a definite diagnosis of PE by showing the outline of the thrombus in a pulmonary artery. It requires only an intravenous injection of contrast material, and, therefore, is safe for most patients. Several small investigations have shown marked differences in the sensitivity of spiral CT for the detection of acute PE. In view of the potential applicability of spiral CT, this investigation is proposed to study its role in the diagnosis of venous thromboembolic disease.